In the production of viscous hydrocarbons such as heavy crude, or bitumen from tar sands, it is necessary to thermally stimulate the relatively viscous hydrocarbon material such that it can flow and be withdrawn from the substrate as an emulsion. Usually, thermal stimulation comprises the introduction of hot aqueous heating mediums such as pressurized steam, into the substrate by way of an injection well to contact the bitumen.
This stimulating step over a period of time fluidizes the bitumen and releases it from the tar sand. The steam also establishes a pressure front whereby to urge the now flowable hydrocarbon emulsion or mixture toward one or more production wells.
The present method and apparatus are applicable to producing either bitumen from tar sands, or heavy viscous crude oil from a reservoir thereof within the substrate. To simplify the following description, only bitumen will be referred to as the produced material.
Since the hot steam will condense under proper conditions, the product formed by the bitumen comprises in essence an aqueous mixture. Although this said product could be considered as being an emulsion, depending on the condition thereof, it will be hereafter referred to as an aqueous bitumen mixture.
In one method adapted to this type of viscous hydrocarbon production, it is found practical to utilize a single well which is sequentially heated and produced on the cyclical principle. More specifically, the environment around the well is initially preheated to put the bitumen into a flowable state. Thus, during a soak period, heat is absorbed into the substrate about the well causing the hot flowable material to gravitate toward the well. Thereafter, the stimulating step is continued in such manner that the hot mixture will continue to flow and to be produced from the well.
When over a period of time, pressure within the substrate deteriorates or the production flow decreases, it is necessary to recommence the cycle by further introduction of stimulating medium. As a sufficiently high pressure is reestablished and the bitumen solution is again caused to flow, steam injection is discontinued or minimized. Further controlled draw-down of the bitumen mixture can now be resumed.
This cyclical process can be continued indefinitely until the substrate adjacent to the well becomes exhausted of producible hydrocarbon product. Because of its general character, the method is referred to generally as the huff and puff process. It is found to function efficiently particularly when the stimulating medium is steam.
In an alternate method for producing viscous hydrocarbons from this type of substrate, a plurality of generally vertical wells are drilled in a desired surface pattern. Thereafter, a stimulating fluid such as steam is injected over a period of time into the substrate through a centrally located injector well.
The heated or stimulated area about the well will be progressively widened, thereby establishing a pressure front which drives flowable bitumen mixture toward the surrounding producing wells.
This process enjoys the advantage of being practiced by the continuous introduction of the hot stimulating medium. It thus yields a continuous out- flow.
It is found desirable toward achieving an improved bitumen production rate, to utilize a generally horizontally disposed well for producing from a relatively thin hydrocarbon containing layer. Due to the nature of this type of well, the latter must as herein noted operate on a cyclical basis to achieve an appreciable outflow of bitumen mixture. Since cyclical operation amounts to a disruption of the producing phase it constitutes a less than economical expedient.
To realize an improved production rate from a horizontal well of the type contemplated, there is presently provided an efficient method and apparatus for producing a hot aqueous bitumen mixture from a tar sand or similar environment. The process is effectuated through a single, elongated horizontal well which lies in at least a portion of a tar sand layer, preferably in a direction concurrent with the layer's direction.
Both the horizontal well itself and the adjacent substrate, are initially preheated to establish a favorable operating temperature at which fluidized bitumen mixture becomes mobile. The well includes means to establish a pattern of paths through the productive layer along which the bitumen mixture will readily flow. Said paths thereby communicate a relatively high pressure injection area where the stimulating fluid is introduced, with the low pressure area in the well toward which the bitumen gravitates.
Thereafter, and subsequent to the preheating step, the horizontal well is produced by regulated further introduction of hot stimulating fluid. This latter injection, together with control of the well back pressure, causes fluidized bitumen mixture to be urged toward the well producing end. At high temperature conditions, and after a period of operation, all or a part of the stimulating steam will be produced with the mixture, thereby giving an indication of a decrease in the production rate.
To maintain a favorable production output, the substrate is most effectively swept clean of removable bitumen by adjusting the injection pattern of stimulating fluid. The latter is achieved by diverting the flow of the stimulating steam whereby to change the relationship between the high pressure or injection under the well liner, and the low pressure or production end thereof.
It is therefore an object of the invention to provide a method and apparatus for improving the production of viscous hydrocarbon fluid from the subterranean reservoir in which the hydrocarbon fluid is locked. A further object is to provide a method and apparatus for stimulating and producing a well aligned substantially horizontally in the formation, and containing a relatively viscous hydrocarbon. A still further object is to provide a method and apparatus for the continuous production of a viscous hydrocarbon fluid from a single well disposed substantially horizontally through a productive formation.